Crematogaster torosa ants form polydomous nests and outstations independently of food distance

Polydomy, in which one ant colony maintains multiple, spatially segregated nests that routinely exchange workers and brood, is a common nest structure. However, ants also build a number of intermediate structures, including “outstations” that contain workers but no brood. Although little is currently known about the function of outstations, they may increase foraging efficiency of colonies by shortening foraging distances. In this study, we investigated whether Crematogaster torosa colonies created outstations or polydomous nests in response to consistently available food at different distances from the queenright nest. At least some workers moved closer to food in all 21 colonies tested. Fourteen colonies became polydomous by moving both workers and brood, while the remainder moved only workers and formed outstations. The proportion of ants moved decreased significantly with increasing distance to food, but there was no effect of distance on whether colonies formed outstations or polydomous nests. Nests that contained at least 19% of the total workforce also contained brood. Workers marked while traveling between the nests or outstations were more likely to be recaptured in the original queenright nest arena, but workers marked while collecting food were more likely to be recaptured in the arena containing the new nest or outstation. Crematogaster torosa appears to have a flexible colony structure, readily forming both outstations and polydomous nests in response to food. Although nests and outstations differ in whether they contain brood, they appear to serve many similar functions in this species.